The former London mayor’s decision not to join the battle leaves Home Secretary Theresa May as hot favourite to be the next Prime Minister.

It came after the shock announcement by fellow Brexit campaigner Michael Gove - who had widely been expected to be Mr Johnson’s running mate - that he was putting himself forward for the leadership.

In a dramatic press conference just moments before the deadline for nominations passed, Mr Johnson said that the next Tory leader would have to unify his party and ensure that Britain stood tall in the world.

And he said: “Having consulted colleagues and in view of the circumstances in Parliament, I have concluded that person cannot be me.”